In the prior art of which the inventor is aware, mobile and other paper shredders typically use knuckle type devices to shred paper. So far as the inventor is aware, mobile paper shredders, other than those made by the inventor, achieve shredding rates of less than 2000 lbs per hour. The slow rate is believed to be due to the use of slowly rotating pairs of shafts.
In a mobile paper shredder used commercially in secret by the inventor and his company in the United States more than one year before the filing of this application, the inventor used a mobile paper shredder using a hammer mill for the shredding of the paper. The hammer mill included rotating hammers mounted on a horizontal axis, with the horizontal axis below a lower confining surface of a tub. The hammers rotated up into the tub and down in an opening in the tub, past impact surfaces located on a side of the opening. Paper caught between the hammers and the impact surfaces was shredded. Paper was fed to the opening along the lower confining surface of the tub. At impact, the striking angle was greater than 30.degree.. The striking angle in a hammer mill is the angle between the direction of movement of the hammer at the point of impact with paper being shredded and the direction it is desired to send the shredded paper, that is towards a discharge bin or chute. Since the direction of feed of shredded paper is normally at right angles to the direction of ejection of shredded paper, this is typically equivalent to the angle between the long axis of the hammers and the direction of feed.
This design, with a striking angle greater than 30.degree., proved moderately successful, but was subject to jamming as the hammers moved past the impact surfaces. This is believed to be due to the hammers imparting a component of movement to the paper in the direction of the impact surfaces, and therefore leading to bunching of paper between the impact surfaces and the hammers, thus jamming the hammers. For a striking angle greater than 30.degree., the force imparting a component of movement in the direction towards the impact surfaces is greater than one-half the force tending to shear the paper.
The inventor proposes a novel construction of a paper shredder believed to be able to achieve a shredding rate of up to 8,000 lbs per hour. In one aspect of the invention, a paper shredding apparatus including a paper feeder, paper shredder with hammers and shredded paper unloader has its hammers mounted at a striking angle of less than 30.degree.. It is desirable that the striking angle be as low as possible (near zero). However, the limitation that the axle on which the hammers are mounted be lower than the lower confining surface of the tub limits the angle to about 10.degree. to 20.degree. in many practical situations.
Further improvements have also been made to the design of the previously used paper shredder to increase the throughput of the paper shredder.
Thus, in one aspect of the invention, the feeder has a lower confining surface forming a predominantly horizontal plane, the horizontal axis on which the plural hammers are mounted lies below the horizontal plane; and the direction of feed is along the lower confining surface of the feeder towards the opening in the shredder.
The unloader preferably includes a bin formed of a base, first and second sidewalls spaced from each other and separated by the base, a reciprocating end wall disposed between the first and second sidewalls, and an upwardly extending discharge chute opposed to the reciprocating end wall; and a motor operatively connected to the reciprocating end wall such that reciprocation of the end wall compacts shredded paper within the bin and forces it out of the discharge chute.
The unloader may further include a shredded paper storage area bounded by walls, one of the walls being openable and forming an unloading gate, and one of the walls being movable across the storage area towards the openable wall, the discharge chute disposed to discharge paper into the storage area through one of the walls.
The paper feeder preferably includes a tub formed of an encircling wall, and a lower and upper confining surface, the inlet of the feeder being formed in the upper confining surface and the outlet being formed in the lower confining surface, the paper feeder including a sweeping arm mounted for rotation in the tub and to sweep across the lower confining surface between the encircling wall.
The paper shredder preferably includes a lifting arm mechanism for lifting and rotating initially upright paper containers to empty the paper containers into the paper feeder, the lifting arm mechanism including a lifting arm mounted about a horizontal axis and rotatable from a lower position for attaching a paper container onto the lifting arm to an upper discharge position, the lifting arm having a free end, a detachable latch for a paper container on the free end of the lifting arm, and means to rotate the paper container into an emptying position.
There is also preferably included according to a further aspect of the invention a governor connected to the paper feeder to regulate feeding of the rate at which paper is fed into the paper shredder.
According to an aspect of a method according to the invention, the following steps are included: feeding paper into a paper shredder mounted on a motor vehicle; shredding the paper to produce shredded paper; compacting the shredded paper to produce compacted shredded paper; and periodically moving the compacted shredded paper towards and out of the unloading gate.
According to a further aspect of the method, feeding the paper includes feeding the paper into the paper shredder along a direction of feed; and shredding the paper includes impacting the paper with hammers whose striking angle is less than 30.degree..
According to a still further aspect of the method of the invention, the paper shredder is located in a lower confining surface of a tub and feeding the paper into the paper shredder includes loading paper into the tub by lifting the paper in a paper container on a lifting arm to a point above the tub, and rotating the paper container to discharge the paper into the tub.
Feeding the paper into the paper shredder preferably includes moving paper in the direction of feed with a rotating arm mounted on a central vertical axis in the tub. Compacting the shredded paper preferably includes, according to a still further aspect of the invention, depositing shredded paper in a bin formed of a base, first and second sidewalls spaced from each other and separated by the base, a reciprocating end wall disposed between the first and second sidewalls, and a discharge chute opposed to the reciprocating end wall; and reciprocating the end wall towards and away from the discharge chute.
Periodically moving the compacted shredded paper includes according to a still further aspect of the invention depositing compacted shredded paper on one side of a moving wall; and periodically moving the moving wall towards the unloading gate. Preferably, the shredder is a hammer mill and the rate of feed of paper into the hammer mill is regulated.